A number of power transmission belts having a variety of grooved constructions are known. U.S. Pat. No. 4,011,766 discloses a belt consisting of multiple belt elements connected with a tie band. The individual elements have transverse grooves perpendicular to the sides of the belt. The grooves on adjacent belt elements are staggered and, optionally, spaced differently to eliminate hinge points and provide some noise randomization. There is no attempt made to minimize the noise generated by each individual belt element. While this concept is practical for belts constructed of individual belt elements which can have the grooves formed prior to assembly, it is not practical for multi-ribbed belts which are built as a single unit and machine formed, which is currently the state of the art method for forming most automotive and industrial multi-ribbed belts.
U.S. Pat. No. 4,034,615 discloses a single V-belt having angled grooves. While this reduces the noise generated by each groove, it does not provide the noise cancellation that can be achieved by having multiple sources of the same frequency operating out of phase with each other. Additionally, this patent does not disclose multi-ribbed belts.
U.S. Pat. No. 5,055,090 discloses grooved multi-ribbed belts having randomized grooved spacing and/or depth. While this serves to distribute the noise over a wider frequency range, it does not significantly reduce overall noise. In addition, this method is at a disadvantage to the helical groove design, because some grooves are longer or shallower than would be optimum for maximum flex life. The long or shallow grooves have higher stress concentrations and are the first areas to crack or chunk out. Finally, the grooves are perpendicular to the bending direction, creating hinge points. This increases the tendency of single rib cracks to propagate across the entire belt width.
U.S. Pat. No. 5,209,705 discloses a single synchronous drive belt having at least two adjacent rows of teeth which are at oppositely balanced oblique angles to the longitudinal direction of the belt. In addition, the center lines of the teeth in the adjacent rows are offset from each other by a distance of up to 10% to 90% of their pitch.
U.S. Pat. No. 5,211,608 discloses a positive drive timing belt having spiral grooves cut into the teeth in order to allow air pockets to escape in all directions.
The invention being disclosed herein improves on the prior art by optimizing noise cancellation by controlling the phase angle between the noise sources of each individual rib and reducing the noise generated by each rib by setting transverse grooves at an angle other than perpendicular to the longitudinal direction of the belt. It further uses a constant transverse groove depth to equalize the stresses on each groove and to eliminate any hinge points.